The invention relates to a device for document filming with optional illumination of the original from above or below according to choice, light sources of different spectral radiation characteristics being provided for the two types of illumination.
Conventionally, illumination from above uses a source vertically above the original, the camera receiving light reflected from the original. Illumination from below causes the camera to receive light transmitted through the original.
For the filming of transparent originals it is usual to illuminate the original either from above or from beneath. If light sources of equal spectral radiation characteristics, for example incandescent lamps are used for the two types of illumination, the adaptation of the spectral sensitivity of a photo-receiver to the spectral sensitivity of the film can be achieved by simple arrangement of a colour filter. If on the other hand light sources of different spectral radiation characteristics are used, for example incandescent lamps for illumination from above and fluorescent tubes for illumination from below, then the spectral adaptation of the photo-receiver to the different radiation characteristics of the two light sources cannot be achieved to the requisite extent by the arrangement of a colour filter. Therefore the indication of the exposure meter will lead to different darkening of the film for illumination from above and compared with illumination from below.
The invention is based on the problem, in a camera of the initially stated kind, despite deviation in the spectral adaptation between film and photo-receiver, of obtaining an exposure indication which leads to equal darkening of the film in the case of different radiation characteristics of the light sources for illumination from above and illumination from below respectively.